1. Field of the Invention
The present invention relates to a ceramic electronic component and a method for manufacturing the same, and specifically to an external electrode of the ceramic electronic component and a process for forming the external electrode by plating.
2. Description of the Related Art
A monolithic ceramic capacitor, which is known as a representative of ceramic electronic components, includes a multilayer composite including a stack of a plurality of dielectric ceramic layers and a plurality of internal electrodes extending along interfaces between the dielectric ceramic layers, and a plurality of external electrodes each electrically connecting the internal electrodes exposed at a surface of the multilayer composite. Such a known monolithic ceramic capacitor is shown in FIG. 3.
Referring to FIG. 3, the external electrodes are each formed on a surface of the multilayer composite 102 at which the internal electrodes 104 or 105 are exposed, thus electrically connecting the internal electrodes 104 or 105. In order to form the external electrodes, in general, a metal paste containing a metal component and a glass component is applied onto the surfaces at which the internal electrodes are exposed. The coatings of the metal paste are fired, thus forming paste electrode layers 106 and 107.
Then, Ni-based first plating layers 108 and 109 are formed over the surfaces of the paste electrode layers 106 and 107, respectively, and then Sn-based second plating layers 110 and 111 are formed over the surfaces of the respective first plating layers 108 and 109. Hence, the external electrode has a three-layer structure including the paste electrode layer, the first plating layer, and the second plating layer.
The external electrode requires high solder wettability when the monolithic ceramic capacitor is mounted on a substrate with solder. In addition, the external electrode is intended to electrically connect the electrically isolated internal electrodes to each other. The Sn-based second plating layers 110 and 111 ensure sufficient solder wettability, and the paste electrode layers 106 and 107 electrically connect the internal electrodes to each other. The first plating layers 108 and 109 act as the respective underlayers of the second plating layers 110 and 111 to prevent the corrosion by solder used for mounting.
Unfortunately, the paste electrode layers 106 and 107 have a thickness as large as several tens micrometers to several hundred micrometers. In order for the monolithic ceramic capacitor to satisfy certain dimensional specifications, the effective volume of the paste electrode layer must be reduced to ensure a sufficient capacitance while the volume of the paste electrode layer is maintained. On the other hand, plating layers generally have thicknesses as small as several micrometers. If the external electrode can be composed of only the first plating layer and the second plating layer, a larger effective volume can be achieved.
For example, in a multilayer composite disclosed in Japanese Unexamined Patent Application Publication No. 63-169014, electroconductive metal layers are formed by electroless plating over the respective entire side surfaces at which the internal electrodes are exposed, and thus short-circuit the internal electrode layers exposed at the respective surfaces. However, the electroconductive metal layer formed by electroless plating does not have sufficient adhesion to the side surfaces. This may cause a problem with reliability.
In Japanese Unexamined Patent Application Publication No. 05-343259, an external electrode having high adhesion is formed by coating a surface of a ceramic body with an electroless plating layer containing glass powder.
In the production process of this external electrode, however, a blister is liable to be formed at the surface of the plating layer by heat treatment performed after electroless plating, depending on the conditions of the heat treatment. The blister can cause moisture permeation to degrade the reliability, and besides degrades the appearance.
In addition, if the glass particles and the plating metal are co-deposited in this process, the glass is not sufficiently deposited undesirably. Also, the glass can undesirably be melted and lost in a plating bath.